1. Field of the Invention
This invention relates to apparatus for purifying contaminated liquids and, more particularly, to apparatus for electrochemical purification of contaminated liquids. The invention is useful in purifying a liquid contaminated with an organic matter, mechanical admixtures, surfactants and so on. The instant invention is best suited for purifying liquids contaminated with petroleum cuts, such as waste waters containing polymers, oils, and greases.
2. Description of the Prior Art
Among the prior art apparatus for purifying contaminated liquids apparatus for electrochemical purification of liquids are finding ever increasing application due to a wide scope of processing offered by these apparatus and in particular the apparatus for practicing the electroflotation and the electrocoagulation methods.
Known in the art are apparatus for batch and continuous electrochemical purification of liquids. The latter type appears to be more promising.
A prior art apparatus for electrochemical purification of contaminated liquids (USSR Inventor's Certificate No. 407.844) comprises a settling chamber communicating with an electrocoagulation chamber disposed within the settling chamber, both supplied with electrolyte. The electrocoagulation chamber has soluble electrodes and an inlet pipe for contaminated liquid, disposed under these electrodes. The settling chamber is provided with an outlet pipe for a pure liquid. In the process of purification, the contaminated liquid together with electrolyte additions (NaCl, HCl) passes the soluble electrodes which are energized. The metal of the soluble electrodes forms hydroxides which coagulate the impurities present in the contaminated liquid. The liquid passes from the electrocoagulation chamber to the settling chamber where sludge separates from the liquid, and both the sludge and the liquid are discharged by way of different flow paths. When the liquid being purified passes by the electrodes, it contaminates them, which speeds up the passivation of the electrodes and, hence affects the performance of the purification process and necessitates frequent cleaning of the electrodes and, finally, performance of the apparatus is impaired.
Known in the art is an apparatus (Japanese patent publication No. 52-14397) wherein the coagulation chamber is used only to produce a coagulating agent by supplying pure electrolyte thereinto, while the purification process is carried out in another chamber which is supplied with contaminated liquid to produce a mixture with the electrolyte containing the coagulating agents and supplied from the electrocoagulation chamber.
Such arrangement provides for a substantial reduction in deposits on the electrodes. However, the coagulating and flotating capacity of the electrodes is inadequately used in that the process of producing coagulating agents and passage of the electrolyte containing these agents from the electrocoagulation chamber to the settling chamber is accompanied by forming the coagulating agents into aggregates (hydroxides of the metal of the soluble electrodes and gas bubbles forming on the surface of the soluble electrodes), which leads to a decrease in the specific surface and, consequently, in coagulation and flotation capacity of the electrodes.
Known in the art is an apparatus for electrochemical purification of waste waters (USSR Inventor's Certificate No. 644,378), comprising a settling chamber with an electrocoagulation chamber coaxially disposed within the same settling chamber. The apparatus is provided with inlet and outlet pipes for water, an inlet pipe for the supply of electrolyte into the electrocoagulation chamber.
In the lower portion of the electrocoagulation chamber there are soluble electrodes producing ions of their metal under the action of an electric current, which ions attach to the hydrolyzates and form metal hydroxides.
The metal hydroxide is carried up by gas bubbles from the interelectrode space to the zone of supply of contaminated liquid into the electrocoagulation chamber, and by contacting the impurities thereof it coagulates them into aggregates which are carried up along the electrocoagulation chamber.
In such an apparatus the impurities of contaminated liquid are coagulated with an excess quantity of metal hydroxides. A part of them does not manage to react with the impurities of the contaminated liquid, so it is mixed with foam and discharged from the apparatus. The other part of the hydroxide, some 7 to 18%, which does not react with the impurities of the contaminated liquid, flows together with the liquid from the electrocoagulation chamber to the settling chamber and being entrained by the flowing liquid leaves the apparatus. Some impurities, along with the hydroxides, find their way to the settling chamber as well. The liquid flows to the settling chamber directly along the surface of the electrocoagulation chamber and further takes the volume of the settling chamber mostly in the lower and the middle portion thereof. Such quantity of, about 10 to 20 mg/l, metal hydroxides impairs performance of the liquid purification process and increases specific consumption of the electrodes and power.